The unique physiological and biochemical properties of the kidneys make them a target for a variety of nephrotoxic insults. While there are numerous reports describing events associated with toxicity, many basic questions regarding mechanisms of nephrotoxicity remain unanswered; such as, whether toxicity results from in situ activation to a toxic metabolite, or from metabolites generated elsewhere systemically, or from some physiological or biochemical uniqueness of the kidney resulting in selective accumulation of a toxicant. Such information may provide alternatives to alleviate the nephrotoxicity of therapeutically beneficial drugs. The primary goal of this project is to develop an in vitro model for evaluating mechanisms of nephrotoxicity for acutely acting toxicants. Initial emphasis will be on agents which are toxic to the proximal segment of the nephron and two basic approaches will be employed. The first approach uses renal cortical slices exposed to nephrotoxicants in vitro. Techniques are being developed to assess nephrotoxicity to slices by monitoring physiological and biochemical parameters of renal function analogous to those methods used after in vivo exposure to a nephrotoxicant. Since nephrotoxicants often selectively damage specific cells along the nephron, the second approach involves developing techniques to isolate specific cells from the nephron. Initially, emphasis will be on isolating cells from the pars recta (straight or S3) region of the proximal tubule. These cells are damaged selectively by renal ischemia and by compounds such as cysteine and glutathione conjugates of certain haloalkenes (i.e., hexachloro-1,3-butadiene), mercuric chloride and cis-platinum. The successful development of an in vitro model for nephrotoxicity will have other important applications, such as providing a rapid and inexpensive target organ screen for compounds of unknown toxicity. Additionally, since relatively small amounts of tissue are required for this in vitro model, it may be possible to assess better the relevance of acute animal models for human nephrotoxicity by evaluation of human renal tissue under similar in vitro conditions.